Method for grinding a workpiece

ABSTRACT

A method of modifying a workpiece such as a geared member includes grinding the workpiece with a rotating grinding wheel, and superimposing a primary motion of the axis of rotation of the grinding wheel with a secondary, oscillatory motion of the axis of rotation. The primary motion is oriented perpendicular to the axis of rotation. A motorized apparatus for modifying a workpiece includes a workpiece holding device, a grinding wheel which rotates about a first axis, and the first axis rotating about a second axis, wherein the workpiece holding device and the grinding wheel are moved toward each other in a direction of feed normal to the first axis and permitting a radial face of the grinding wheel to grind against the workpiece via intermittent contact.

TECHNICAL FIELD

The present disclosure relates generally to methods and relatedapparatuses for grinding a workpiece, and relates more particularly to amethod and apparatus whereby primary and secondary relative motions of agrinding wheel are superimposed while grinding the workpiece.

BACKGROUND

Grinding, polishing and related forms of workpiece modification areintegral parts of many manufacturing processes. Developing a particularsurface finish, for example, is often necessary for optimal functioningand/or fitting of manufactured parts. Similarly, the abrasive removal ofmaterial from the exterior of a workpiece is often a preferred way ofensuring that components are dimensioned within required tolerances.Various sanders, grinding belts and grinding wheels are widely used forpost-production modification of parts, to render the parts into afinished state suitable for an end use or further modification.

As an example, metallic gear components, such as gear wheels and gearracks, are sometimes modified by grinding following an initial formingstep such as casting, milling, cutting, forging, etc. A final formingstep such as grinding with a rotating grinding wheel achieves thenecessary surface finish and tolerances that may be required for aparticular gear application. This final grinding step can be crucial forensuring that the gear components are capable of meshing together andoperating in a desired manner. Besides using grinding as a finishingoperation in gear production, grinding is also sometimes used to roughform complex gear tooth profiles may not be cost effectively roughformed with other rough forming processes such as hobbing or milling.While grinding has been shown to be quite effective and reliable in theproduction of gears and other types of components, there are someinherent difficulties and challenges relating to the use of grinding.

For example, a rotating abrasive grinding wheel modifies the surface ofa metallic part, such as a gear, by removing tiny chips of material viaabrasives adhered to the surface of the grinding wheel, or incorporatedinto the material matrix of which the wheel is composed. These chipstend to “clog” the grinding wheel in that they often weld or otherwiseadhere to the wheel after removal from the workpiece. Upon subsequentcontacting of the grinding wheel surface with the workpiece some of theabrasive material can be obscured by the adhered chips, and the grindingeffectiveness can be compromised. Engineers have addressed this problemby removing the adhered material with a high-pressure fluid spray. Thefluid pressure must typically be quite high to successfully remove thechips from the grinding wheel surface. It is also common to use adressing tool to scrape off chips of material, sharpen dull grains andalso to reform the exterior of the grinding wheel, as its shape may wearwhen material is removed from the grinding wheel itself. The scraping ofthe wheel is known in the art as “dressing” or “redressing.” Grinding,especially with large depth of cut requires great amounts of energy andfluid flow to support a grinding operation.

Another problem in many grinding processes relates to the heat generatedby frictional forces between the rotating grinding wheel and the surfaceof the workpiece. The heat, which is often relatively intense, istypically dissipated in part through coolant fluid. However, the volumeof fluid that must be sprayed onto the rotating grinding wheel andworkpiece tends to be relatively large, often on the order of hundredsof gallons per minute for certain grinding processes. In addition, therelatively high amounts of heat that must be dissipated from the fluidrequire a relatively large and sophisticated heat exchanger/chillersystem and often require substantial floor space and energy demand tosupport a grinding operation. In some instances, the fluid flow andcooling apparatus occupies more space on a factory floor than thegrinding machine it supports. High heat loads further require arelatively lengthy process time for grinding a workpiece, to preventthermal damage to the workpiece (grind burn).

Moreover, the grinding wheel itself must typically be relatively porousto allow space for chips and fluid to be transported through the contactlength between the wheel and the workpiece. Higher grinding wheelporosity generally results in decreased stiffness, higher cost and arelatively shorter working life of the grinding wheel. Such grindingwheels are also typically larger making the contact length longer thanwhat it ideally could be, and thus make the grinding forces higherrequiring relatively robust bearing supports and powerful drive motors.

One known gear grinding method is discussed in U.S. Pat. No. 4,780,990to Cody, Jr. et al. Cody, Jr. et al. describe a method and machine forforming longitudinally curved tooth surfaces in bevel and hypoid gears.The machine of Cody, Jr. et al. includes a dish-shaped grinding wheelrotated about its axis, and also about a parallel cradle axis in a timedrelationship with a reciprocating work gear. Cody, Jr. et al. recognizethat rotating a grinding wheel while oscillating it through an arccorresponding to desired gear tooth shape can promote coolant accessbetween the gear and grinding wheel, however, the disclosed design andmethod is applicable only to certain gear types, and is relativelycomplex.

The present disclosure is directed to one or more of the problems orshortcomings set forth above.

SUMMARY OF THE DISCLOSURE

In one aspect, the present disclosure provides a method of modifying aworkpiece, including grinding the workpiece with a rotating grindingwheel. The method further includes, while grinding the workpiece, movingthe axis of rotation of the grinding wheel relative to the workpiece ina primary feed motion along a path oriented perpendicular to the axis,wherein moving the axis of rotation includes superimposing onto theprimary motion a second, oscillatory motion of the axis relative to theworkpiece.

In another aspect, the present disclosure provides a method of grindinga profiled form member, including grinding at least one groove in themember with a rotating grinding wheel. The method further includes,moving the axis of rotation of the grinding wheel relative to the memberin a feed direction oriented perpendicular to the axis, including movingthe axis via an oscillatory motion thereof relative to the member.

In still another aspect, the present disclosure provides a motorizedapparatus for grinding a workpiece, including a workpiece holding devicewhich holds thereon a workpiece to be modified. The apparatus furtherincludes a grinding wheel which rotates about a first axis, the grindingwheel having a radial face and two opposed axial faces, each of theaxial faces having a circumferential edge being joined to the other bythe radial face. The first axis rotates about a second axis that isgenerally parallel to, and offset from, the first axis, wherein theworkpiece holding device and the grinding wheel are moved toward oneanother in a direction of feed that is normal to the first axispermitting the radial face to grind against the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned side view of a portion of a motorizedapparatus for modifying a workpiece according to one embodiment of thepresent disclosure;

FIG. 2 is a side view of a portion of a motorized apparatus formodifying a workpiece according to another embodiment of the presentdisclosure;

FIG. 3 is a partially sectioned end view of a portion of the apparatusof FIG. 1, taken along line 3-3;

FIG. 4 is a side diagrammatic view of a portion of a motorized apparatusfor grinding a workpiece according to another embodiment of the presentdisclosure;

FIG. 5 is a schematic illustration of a workpiece engaged with agrinding wheel via a process according to the present disclosure; and

FIG. 6 is a partially sectioned side view of a portion of a motorizedapparatus for modifying a workpiece according to another embodiment ofthe present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown an apparatus 10 forgrinding/modifying a workpiece W₁ in accordance with one embodiment ofthe present disclosure. Apparatus 10 includes a body 14 coupled with agrinding wheel drive motor 12, and rotatably supporting a driveshaft 16coupled with a grinding wheel 40. Spindle 16 may also be driven by meansof gears or belts with the motor mounted on housing 14. Grinding wheel40 may be rotated as described herein to modify workpiece W₁. W₁ may bea profiled form member such as a gear wheel or gear rack, or it might besome other type of workpiece. In one embodiment, it is contemplated thatworkpiece W₁ may be a preformed metallic geared member formed via acasting, forging, machining, etc. process. Referring briefly to FIG. 6,there is shown another embodiment of an apparatus 210 according to thepresent disclosure, wherein numerals alike to those of FIG. 1 are usedto identify similar features. Apparatus 210 differs from apparatus 10 ofFIG. 1 in that first and second similar body portions 14 a and 14 b aredisposed on opposite sides of a grinding wheel 40, and each rotatablysupport shaft 16. It is contemplated that in most embodiments a singlebody portion, on only one side of grinding wheel 40 will be used.However, in other instances dual body portions as shown in FIG. 6 couldbe used to provide additional support for grinding wheel 40.

Returning to FIG. 1, a fluid spraying assembly 30 having a set ofnozzles may be positioned proximate grinding wheel 40 to apply a fluidspray to the grinding wheel for removing material chips welded orotherwise adhered to the grinding wheel and to cool the same. A scrapersuch as a diamond dressing roller (not shown) may also be provided tocontact grinding wheel 40 continuously or intermittently, and operableto “redress” the same. For reasons that will be apparent from thefollowing description, the need for dressing of grinding wheel 40 may bereduced as compared to conventional designs.

Shaft 16 will typically be rotatable about a central axis C andjournaled via a first set of bearings 22. Shaft 16 is also disposedwithin an eccentric 20 which is rotatable about another axis E andjournaled by a second set of bearings 24. An eccentric drive motor 13may be coupled with eccentric 20 via an output shaft 15 operable todrive eccentric 20 via a belt 17, for example. Those skilled in the artwill appreciate that a variety of different drive motor configurationsmight be used to rotate shaft 16 and eccentric 20. Moreover, in theembodiment of FIG. 6, for example, rotation of shaft 16 and rotation ofan eccentric disposed on each side of grinding wheel 40 should besynchronized. Axis C and axis E are generally parallel, and axis C thusbeing rotatable about axis E via a rotation of eccentric 20. Varioussuitable means are known in the art for balancing rotating componentssuch as grinding wheel 40 and eccentric 20, including selectively addingor removing weight so that grinding wheel 40 and eccentric 20 willrotate smoothly at relatively high RPM.

Simultaneous rotation of shaft 16 about axis C and rotation of eccentric20 about axis E will allow grinding wheel 40 to rotate against andintermittently contact workpiece W₁ while axis C travels about a pathdefined by the shape/eccentricity of eccentric 20. Distance h denotes arelative offset of axes C and E, in turn defining the radius of the pathtraversed by axis C. Offset h may be a distance less than about 0.02inches, and may in certain embodiments be less than about 0.01 inches.In still further embodiments, offset h may be in the range of about0.001 to about 0.005 inches. In practice, an observer may not be able toperceive the compound motion of grinding wheel 40 merely by watching thegrinding process.

It will generally be desirable to set the relative offset of axes C andE to a distance that shortens the contact length and is sufficient toallow coolant to be pumped between the workpiece and grinding wheel 40,as described herein. However, if the offset between axes C and E is toolarge, undesirable shaking of apparatus 10 may be induced. In onecontemplated embodiment, grinding wheel 40 will rotate about axis C in afirst direction, and axis C will rotate about axis E in an oppositedirection. In other embodiments, the directions of rotation of axis Cand grinding wheel 40 may be the same.

It is contemplated that the absolute value of the ratio of therotational speed of grinding wheel 40 about axis C to the rotationalspeed of axis C about axis E may be in the range of about 0.8 to 1.6,and may further be in the range of about 1.05 to 1.4. In one embodiment,the ratio of the absolute value of the rotational speed of grindingwheel 40 about axis C to the rotational speed of axis C about axis E maybe about 1.2. It will generally be desirable for the rotational speed ofaxis C about axis E to be as fast as is practicable, to minimize theinstantaneous contact length between grinding wheel 40 and workpiece W₁,described herein. The maximum rotational speed of axis C about axis Ewill generally be limited by the capability of the associated bearingsand drive motor, and in certain embodiments the surface speed ofgrinding wheel 40 may be in the range of about 3600 to about 4500 feetper minute. In any event, however, different rotational speeds ofgrinding wheel 40 itself versus the speed of axis C about axis E will bedesirable. If the respective speeds are the same, substantially the sameportion of grinding wheel 40 will repeatedly contact the workpiece ateach revolution, resulting in uneven wear on grinding wheel 40 andreduced wheel life. In one contemplated embodiment, an appropriateorbital speed (RPM) of axis C about axis E may be determined by dividingthe grinding wheel rotational RPM by 1.2.

Also shown in FIG. 1 is an arrow A denoting a primary path of motion ofaxis C of grinding wheel 40, or a “feed direction.” During a grindingprocess, axis C will be moved in a direction of feed, e.g. feeddirection A, which is oriented generally perpendicular to axis C. Feeddirection A will typically be a linear motion, or possibly a curved pathwith a large radius. Feed direction A refers generally to the directionthat workpiece W₁ and axis C of grinding wheel 40 are moved relative toone another during a grinding process. Thus, either or both of theworkpiece and grinding wheel 40 could be moved to create the primarymotion, as well as the secondary, oscillatory motion, described herein.

Grinding wheel 40 will remove material from workpiece W₁ as it rotates,and the removal of material will allow axis C of grinding wheel 40 to bemoved generally along feed direction A toward workpiece W₁. Arrow Brepresents a secondary, oscillatory motion of axis C relative toworkpiece W₁, resulting from the motion of axis C about its path definedby distance h. Thus, the secondary, oscillatory motion will typically bea non-linear motion, although represented in FIG. 1 via arrow B. Duringa typical grinding process, the net motion of grinding wheel 40 will begenerally aligned with arrow A, that is, toward workpiece W₁, however,the net motion will be the result of the primary motion in the feeddirection superimposed with the secondary, oscillatory motion.

During operation, primary loads on shaft 16 resulting from urginggrinding wheel 40 against workpiece W₁, i.e. moving axis C in the feeddirection, will be reacted by bearings 22 and 24. This contrasts withknown apparatuses (e.g. Cody, Jr. et al. discussed above) whereinprimary loads from urging a grinding wheel against a workpiece arereacted by thrust bearings in a direction parallel the grinding wheelaxis of rotation.

Referring now to FIG. 3, there is shown a sectioned view of a portion ofan apparatus 10 taken along line 3-3 of FIG. 1. In FIG. 3, axes C and Eare shown, as well as a rotation direction of shaft 16 via an arrow T.Bearings 22 and 24 are each shown disposed between inner and outerbearing races. Grinding wheel 40 is shown out-of-contact with workpieceW₁, however, also shown in phantom is a line L representing the path ofthe outer edge of grinding wheel 40 which will eventually bring grindingwheel 40 into contact with workpiece W₁ as grinding wheel 40 rotates.Grinding wheel 40 will typically contact workpiece W₁ along a contactpath Y having a path length defined at least in part by the extent ofoffset between axes C and E, the orbital speed and the feedrate. Arrow Drepresents a feed direction whereby workpiece W₁ may be moved relativeto apparatus 10, and hence axis C. Arrow D is perpendicular to feeddirection A shown in FIG. 1, and represents an alternative feeddirection. However, it should be noted that, like feed direction A shownin FIG. 1, feed direction D is perpendicular to axis C as will be thecase in most, if not all embodiments set forth herein. Those skilled inthe art will appreciate that a grinding process according to the presentdisclosure may have more than one feed direction of the workpiecerelative to the grinding wheel. Similarly, a feed direction differentfrom the primary motion directions shown via arrows A and D iscontemplated by the present disclosure, for example, a directionoriented diagonally relative to arrow D shown in FIG. 3.

Turning to FIG. 2, there is illustrated a close-up view of a portion ofan apparatus 10 similar to that of apparatus 10 of FIG. 1. Like numeralsare used in FIG. 2 to illustrate features similar to those of theapparatus of FIG. 1. Apparatus 10 of FIG. 2 includes a grinding wheel40, shown in proximity to a workpiece W₂ having a plurality of radiallyspaced grooves G, for example, preformed grooves formed therein viacasting, forging, machining, etc. of workpiece W₂. Grinding wheel 40 mayinclude at least one outer radial face 42, for instance first and secondfaces 43 and 45 sharing an outer circumferential edge 41. Grinding wheel40 may further include opposed first and second axial faces 46 and 48,each of the axial faces having a circumferential edge 47.Circumferential edges 47 are joined to one another by the at least oneouter radial face 42.

The eccentric path of axis C of grinding wheel 40 will allow radialfaces 43 and 45 to intermittently simultaneously contact side walls S₁and S₂ of groove G. The approximate position of such contact is shown inphantom in FIG. 2. It should be appreciated that rather than having aprofiled outer radial edge such as the dihedral edge 42 shown in FIG. 2,grinding wheel 40 might include a generally flat circumferential edgesurface whereby each point on the surface is located at generally thesame radius from axis C. Similarly, rather than having defined edges 41and 47, the outer radial face might comprise a curved profile smoothlytransitioning to axial faces 46 and 48.

Turning to FIG. 4, there is shown another embodiment of an apparatus 110for modifying a workpiece W₃ in accordance with the present disclosure.The embodiment of FIG. 4 differs from the foregoing embodiments in thatrather than providing a secondary, oscillatory motion via moving theaxis of rotation of a grinding wheel about a non-linear path, anoscillatory motion of the workpiece W₃ itself is used. In particular,apparatus 110 may include mounts 114 for moving a workpiece holdingdevice 112 in an oscillatory manner by moving linkage arms 115 coupledwith mounts 114 supporting workpiece holding device 112 about non-linearpaths while contacting workpiece W₃ with a rotating grinding wheel (notshown). Each of mounts 114 includes a center mount point P to whichlinkage arms 115 are coupled. Linkage arms 115 can be rotated incircular paths about points P to move workpiece W₃ in a path thatdefines a circle, for example. This circular motion may then besuperimposed with a feed direction of the workpiece relative to thegrinding wheel to produce a compound oscillatory motion similar to thatdescribed above with respect to the embodiment of FIG. 1. It should beappreciated that in the embodiment of FIG. 4, the primary motion may begenerated by moving either or both of the workpiece and the grindingwheel.

In a related embodiment, existing worktable position adjustment controlsmay be used to move W₃ in an appropriate manner. Many common grindingmachines utilize Computer Number Control (CNC) to position a workpiecefor grinding. For example, a grinding machine microprocessor may beprogrammed to adjust the left-right position of a worktable (and hence aworkpiece) as well as the up-down position of the worktable in such amanner that the workpiece travels in a non-linear path. Motion alongother axes of such a worktable may also be used to produce the desiredrelative motion between the workpiece and grinding wheel.

In either of the above embodiments involving moving the workpiece toprovide the desired oscillatory motion, the direction, frequency andradius of the travel path defined by the workpiece may be similar to theembodiments described above with respect to FIGS. 1 and 2. Thus, theradius of a circular path traversed by W₃ in the FIG. 4 embodiment maybe determined in a manner similar to determining an appropriate relativeoffset of axes C and E described with respect to the embodiment ofFIG. 1. The frequency and direction of movement of workpiece W₃ aboutsuch a path may also be determined in a similar manner. It should beappreciated that much of the present description will be applicable tothe embodiment of FIG. 4, even if not specifically referred to, as theresults and advantages of grinding a workpiece via the embodiment ofFIG. 4 may be similar to those of the other embodiments describedherein.

INDUSTRIAL APPLICABILITY

Referring to the drawing Figures generally, a process ofgrinding/modifying of a workpiece will typically take place bypositioning a workpiece W₁, W₂ on a workpiece holding device, such as aworktable 50 as shown in FIG. 3. Those skilled in the art will recognizethat a wide variety of suitable known workpiece holding devices exist. Asimple support platform, or any other holding device appropriate for thedesired application may be used. Rotation of grinding wheel 40 aboutaxis C and rotation of eccentric 20 about axis E will also be initiated.Grinding wheel 40 then moves toward and cuts into workpiece W₁, W₂ asapparatus 10 is moved toward holding device 50 in a direction generallyperpendicular to axes C and E.

The secondary, oscillatory motion of grinding wheel 40 may be producedby rotation of eccentric 20 about axis E, causing axis C of grindingwheel 40 to orbit around axis E. This orbiting of axis C causes theouter radial face 42 of grinding wheel 40 to move generally back andforth relative to workpiece W₁, W₂.

The eccentric motion of grinding wheel 40, and hence the correspondingeccentric motion of its outer radial face, will facilitate the reductionof the contact length and pumping of coolant fluid between grindingwheel 40 and workpiece W₁, W₂, in contrast to certain earlier designsfor creep feed and parallel axis gear grinding as described herein. Inother words, rather than a constant contact path which is a segment of acircular line, outer radial face 42 of grinding wheel 40 willalternately plunge toward and away from workpiece W₁, W₂, contacting italong an arcuate contact path having a path length defined at least inpart by the offset between axes C and E. A relatively larger offset maycorrespond generally with a relatively shorter arcuate contact path,although it should be appreciated that the contact path length maydepend also on RPM and feed rate. Each time that grinding wheel 40 isbrought into contact with workpiece W₁, W₂, it may grind a facetthereon. Continuous rotation of grinding wheel 40, and movement of axisC about its path will grind a series of adjacent facets along thecontact path Y resulting in a finished surface. The length of eachindividual facet will be based at least in part on the offset betweenaxes C and E, and could also be based on RPM of axis E and feed rate inthe D direction. A smaller offset may generate relatively longer facets,and vice versa. A relatively faster feed rate may generate longerfacets, whereas a relatively faster RPM may generate relatively shorterfacets.

As grinding proceeds, and material is removed from workpiece W₁, W₂,workpiece W₁, W₂ and grinding wheel 40 will continue to be movedrelative to one another in a selected feed direction. In the context ofa gear rack, for example, grinding wheel 40 might be moved back andforth across the workpiece for multiple passes, each time removinganother layer of material from the workpiece. The use of plural dihedraledge portions, as shown in FIG. 1, will allow multiple grooves of such aworkpiece to be ground at one time. FIG. 2 illustrates grinding of aconventional parallel axis gear. In such an embodiment, the gear may berotated such that grinding wheel 40 is serially engaged with adjacentgrooves until each groove between adjacent gear teeth has been ground.

It is contemplated that the presently described methods and apparatuseswill be particularly well suited to creep feed grinding, for example, ofa gear rack or similar article, and also to parallel axis gear grinding.The present disclosure further provides advantages over known geargrinding and workpiece modifying methods using oscillatory motionswhich, while applicable to certain specific gear types, are unsuitablefor creep feed and parallel axis grinding processes.

Moreover, the present disclosure provides substantial improvements overconventional, non-oscillatory creep feed and parallel axis gear grindingprocesses, which tend to be slow, produce excessive amounts of heat, andrequire complex and expensive apparatuses for dressing and thermalmanagement. By superimposing a primary and a secondary, oscillatorymotion of the grinding wheel axis of rotation, the contact length willbe smaller than in conventional creep feed and parallel axis geargrinding. Chips removed from the workpiece will typically be thicker andshorter, resulting in lower forces between the grinding wheel and theworkpiece. Chips removed from the workpiece are also easier to removefrom the grinding wheel in the wheel cleaning process, as they are lesslikely to weld thereto. This is due at least in part to the lesser heatamount produced due to the shorter contact path of the grinding wheelwith the workpiece. The relatively shorter contact path of the grindingwheel with the workpiece and its intermittent contact therewith alsobetter enables the chips to be cleared from the contact zone as comparedfrom conventional creep feed and parallel axis gear grinding. Theshorter contact length also provides for better cooling given the largeramount of space for coolant to pass between the grinding wheel andworkpiece, and the coolant pumping action of the grinding wheel as itoscillates.

Increased coolant delivery to the contact zone between the workpiece andthe grinding wheel also prevents overheating of the surface of the part,drastically reducing the risk of grinder burn. The grinding wheelsemployed in apparatuses and processes according to the presentdisclosure may also be made less porous than in certain earlier designs,as the amount of fluid that needs to be passed through the grindingwheel is reduced. This allows a more durable grinding wheel to be used,capable of spinning at higher speeds and having a longer working life.The more durable grinding wheel, coupled with easier chip removal canreduce the need for dressing of the grinding wheel. Thus, onlyintermittent contact while grinding, or periodic treatment with adressing roller while the eccentric is locked, for example, may besufficient to maintain grinding wheel 40. Still further advantagesrelate to smaller and less costly supporting hardware, including areduction in the necessary grinding shaft power, including a smallershaft motor, and better management of loads on the shaft, as well as agreater overall apparatus working life given the lower stress and heatlevels.

Faster processing time of parts is also made possible by the presentdisclosure, as less heat goes into the workpiece, reducing the risk ofgrind burn. In the context of parallel axis gears, there is less timerequired between grinding of the first and last tooth, increasing toothspacing quality due to a reduction in thermal differences among theteeth during grinding. Cold working of the part is also possible via theapplication of the grinding wheel at lower temperatures. Where thesubject gear or other part is ground with a relatively cooler grindingwheel, compressive stresses can be introduced into the surface zone ofthe part, analogous to pre-stressing cold forming processes for metalliccomponents known from related technical fields.

FIG. 5 is illustrative of certain of the advantages of the presentdisclosure over known creep feed and parallel axis gear grindingconcepts. In FIG. 5, there is shown schematically a grinding wheel 40engaged with a workpiece W. In FIG. 5, O denotes the center ofoscillation of axis C of grinding wheel 40. The center of oscillation,O, may correspond with the center of rotation of the eccentricassociated therewith (not shown). O may also represent the center ofrotation of axis C in an embodiment such as the embodiment of FIG. 4,wherein the secondary, oscillatory motion is created by moving theworkpiece holding device, 50, 112. Thus, 0 may be thought of as a“virtual” center of oscillation of axis C, even in embodiments whereinaxis C does not physically rotate.

R₁ illustrates a theoretical radius of grinding wheel 40. In otherwords, R₁ may be thought of as the radius of a circle swept by the outerradial face (or edge) of grinding wheel 40 as it makes a completerotation via rotation of the grinding wheel itself and the secondary,oscillatory motion of axis C. R₂ represents an actual radius of grindingwheel 40. Line V represents an approximate depth of grind of grindingwheel 40 in workpiece W, whereas Y denotes the arcuate contact path ofgrinding wheel 40 with workpiece W without the oscillation motion. ArrowZ refers to a direction of rotation of axis C, whereas arrow Tidentifies the direction of rotation of grinding wheel 40. Althoughgrinding wheel rotation is shown opposite to the rotation direction ofaxis C, it should be appreciated that the present disclosure is by nomeans thereby limited. Arrow A represents the feed direction ofworkpiece W relative to grinding wheel 40. In the embodiment shown inFIG. 5, the feed direction is generally parallel the surface ofworkpiece W and perpendicular axis C, although the present disclosure isnot thereby limited, as described herein.

As represented in FIG. 5, the actual length of contact between grindingwheel 40 and workpiece W is less than the total arcuate contact path Y,and a gap X exists at each end of the actual length of contact,resulting from the orbit of axis C about O. Gaps X allow coolant fluidto be distributed between grinding wheel 40 and workpiece W alongarcuate contact path Y, and provide a space whereby chips of materialremoved from workpiece W can be flushed out. During grinding ofworkpiece W, actual contact between workpiece W and grinding wheel 40will proceed along contact path Y. If axis C were not itself oscillatedvia an orbit about O, as in conventional creep feed and parallel axisgear grinding concepts, grinding wheel 40 would contact workpiece Walong the entire arcuate contact length Y, leaving little if any roomfor coolant fluid to pass, hindering chip removal and generatingexcessive heat.

The present description is for illustrative purposes only, and shouldnot be construed to narrow the breadth of the present disclosure in anymanner. Thus, those skilled in the art will appreciate that variousmodifications might be made to the presently disclosed embodimentswithout departing from the intended spirit and scope of the presentdisclosure. For instance, while much of the foregoing descriptionrelates to grinding processes for metallic gears, the present disclosureis by no means thereby limited. A multiplicity of other workpieces andworkpiece modification processes may benefit through the application ofthe present disclosure. Rather than a gear grinding process, the presentdisclosure contemplates an apparatus and method for grinding/modifying asurface on other types of workpieces. Further, the workpiece need not bemetallic but instead might be wood, a composite or some other type ofmaterial, and need not be a geared member but could be some other typeof profiled member or a member that is not profiled at all. Otheraspects, features and advantages will be apparent upon an examination ofthe attached drawings and appended claims.

1. A method of modifying a workpiece comprising: grinding the workpiecevia a plurality of passes with a rotating grinding wheel, includingmoving an axis of rotation of the grinding wheel back and forth relativeto the workpiece; and while grinding the workpiece, moving the axis ofrotation of the grinding wheel relative to the workpiece in a primarymotion along a path oriented perpendicular to the axis, wherein movingthe axis of rotation includes superimposing onto the primary motion asecondary, oscillatory motion of the axis relative to the workpiece. 2.The method of claim 1 wherein superimposing onto the primary motion asecondary, oscillatory motion comprises superimposing onto a linearmotion a non-linear motion of the axis of rotation of the grindingwheel.
 3. The method of claim 2 wherein grinding the workpiece comprisesurging an outer radial portion of the grinding wheel against theworkpiece.
 4. The method of claim 3 wherein the grinding wheel includesa driveshaft, the method further comprising reacting primary loads onthe driveshaft via journal bearings disposed about the driveshaft. 5.The method of claim 3 wherein the outer radial portion comprises atleast one dihedral edge pointing outwardly from the axis of rotation ofthe grinding wheel, and wherein grinding the workpiece comprisescontacting the at least one dihedral edge therewith.
 6. The method ofclaim 5 wherein the workpiece comprises a geared member having at leasttwo gear teeth, and wherein grinding the workpiece comprises contactingthe at least one dihedral edge with the workpiece along an arcuatecontact path between the at least two gear teeth having a path lengthdefined at least in part by a radius of a circular path of the axis ofrotation defining the secondary, oscillatory motion.
 7. The method ofclaim 6 wherein grinding the workpiece further comprises intermittentlycontacting the at least one dihedral edge simultaneously with side wallsof a groove between the at least two gear teeth.
 8. The method of claim3 further comprising dressing the grinding wheel while grinding theworkpiece.
 9. A method of grinding a profiled form member comprising:grinding at least one groove in the member via a plurality of passeswith a rotating grinding wheel, including moving an axis of rotation ofthe grinding wheel back and forth relative to the member; and moving theaxis of rotation of the grinding wheel relative to the member in a feeddirection oriented perpendicular to the axis, including moving the axisvia an oscillatory motion thereof relative to the member.
 10. The methodof claim 9 wherein the profiled form member comprises a geared member,and wherein moving the axis of rotation comprises moving the axis ofrotation of the grinding wheel via an oscillatory, non-linear motion ofthe axis superimposed onto a linear motion parallel the feed direction.11. The method of claim 10 wherein the at least one groove includes apreformed groove between adjacent gear teeth, and wherein grinding theworkpiece further comprises urging at least one dihedral edge of thegrinding wheel pointing outwardly from the axis against the gearedmember.
 12. The method of claim 11 wherein grinding the workpiececomprises intermittently contacting walls of the groove simultaneouslywith the at least one dihedral edge to form a plurality of adjacentfacets along each of the contacted walls.
 13. The method of claim 11wherein grinding the workpiece comprises grinding a plurality ofpreformed grooves of the geared member via a plurality of dihedral edgesof the grinding wheel pointing outwardly from the axis of rotation. 14.The method of claim 13 wherein grinding the workpiece comprisescontacting the plurality of dihedral edges of the grinding wheel eachwith one of the respective grooves along an arcuate contact path havinga path length defined at least in part by an eccentricity of the axis ofrotation of the grinding wheel.
 15. The method of claim 14 wherein thegeared member comprises a gear rack, the method further comprisingmoving the arcuate contact path of each of the dihedral edges along alength of the grooves, and wherein grinding the at least one groovecomprises grinding a plurality of grooves and moving the axis ofrotation of the grinding wheel back and forth relative to the profiledform member while contacting the plurality of grooves with the rotatinggrinding wheel.
 16. A motorized apparatus for grinding a workpiececomprising: a workpiece holding device which holds thereon a workpieceto be modified; a grinding wheel which rotates about a first axis, thegrinding wheel having a radial face and two opposed axial faces, each ofthe axial faces having a circumferential edge, each circumferential edgebeing joined to the other by the radial face; the first axis rotatingabout a second axis that is generally parallel to and offset from thefirst axis, defining an oscillatory motion of the first axis relative tothe workpiece; and wherein the workpiece holding device and the grindingwheel are moved together in a direction of feed, defining a primarymotion of the first axis upon which the oscillatory motion issuperimposed, that is normal to the first axis permitting the radialface to grind against the workpiece.
 17. A motorized apparatus accordingto claim 16 wherein the grinding wheel rotates about the first axis in afirst direction, and the first axis rotates about the second axis in asecond direction opposite the first.
 18. A motorized apparatus accordingto claim 17 wherein the ratio of the rotational speed of the grindingwheel about the first axis to the rotational speed of the first axisabout the second axis is in the range of 0.8 to 1.6.
 19. A motorizedapparatus according to claim 18 wherein the ratio of the rotationalspeed of the grinding wheel about the first axis to the rotational speedof the first axis about the second axis is in the range of 1.0 to 1.4.20. A motorized apparatus according to claim 19 wherein the ratio of therotational speed of the grinding wheel about the first axis to therotational speed of the first axis about the second axis is about 1.2.21. A motorized apparatus according to claim 16 wherein the first axisis offset from the second axis by a distance less than 0.02 inches. 22.A motorized apparatus according to claim 21 wherein the first axis isoffset from the second axis by a distance less than 0.01 inches.
 23. Amotorized apparatus according to claim 16 wherein the radial face is agenerally flat surface whereby each point on the surface is located atgenerally the same radius from a central axis of the grinding wheel. 24.A motorized apparatus according to claim 16 wherein the radial face isprofiled.